How to enable Logger debug in Log4j

Question

While trying to execute the following lines only the last two statements are displayed  Here is some ERROR  and  Here is some FATAL   and the first three statements are not displayed I had just started to learn this topic  can anyone tell why is this happening       logger debug  Here is some DEBUG        logger info  Here is some INFO        logger warn  Here is some WARN        logger error  Here is some ERROR        logger fatal  Here is some FATAL      the log4j property has   log4j rootLogger debug stdout log4j appender stdout org apache log4j ConsoleAppender log4j appender stdout Target System out log4j appender stdout layout org apache log4j PatternLayout log4j appender stdout layout ConversionPattern   5p   d mm ss   F  M  L  n m n n

User · Answer

I like to use a rolling file appender to write the logging info to a file  My log4j properties file typically looks something like this  I prefer this way since I like to make package specific logging in case I need varying degrees of logging for different packages  Only one package is mentioned in the example   log4j appender RCS org apache log4j DailyRollingFileAppender log4j appender RCS File DateFormat    yyyy-ww  define output location log4j appender RCS File C temp logs MyService log  define the file layout log4j appender RCS layout org apache log4j PatternLayout log4j appender RCS layout ConversionPattern  d yyyy-MM-dd hh mm a   5  c 1   Line  L -  m n log4j rootLogger warn  Define package specific logging log4j logger MyService debug  RCS

User · Answer

You probably have a log4j properties file somewhere in the project  In that file you can configure which level of debug output you want  See this example   log4j rootLogger info  console  log4j appender console org apache log4j ConsoleAppender log4j appender console layout org apache log4j PatternLayout log4j appender console layout ConversionPattern  -4r   t   -5p  c  x -  m n  log4j logger com example debug   The first line sets the log level for the root logger to  info   i e  only info  warn  error and fatal will be printed to the console  which is the appender defined a little below that    The last line sets the logger for com example    if you get your loggers via LogFactory getLogger getClass     will be at debug level  i e  debug will also be printed

User · Answer

You need to set the logger level to the lowest you want to display  For example  if you want to display DEBUG messages  you need to set the logger level to DEBUG   The Apache log4j manual has a section on Configuration

User · Answer

If you are coming here because you are using Apache commons logging with log4j and log4j isn t working as you expect then check that you actually have a log4j jar in your run-time classpath  That one had me puzzled for a little while  I have now configured the runner in my dev environment to include -Dlog4j debug in the Java command line so I can always see that Log4j is being initialized correctly

User · Answer

Put a file named log4j xml into your classpath  Contents are e g    lt  xml version  1 0  encoding  UTF-8    gt   lt  DOCTYPE log4j configuration SYSTEM  log4j dtd  gt    lt log4j configuration xmlns log4j  http   jakarta apache org log4j   gt        lt appender name  stdout  class  org apache log4j ConsoleAppender  gt           lt layout class  org apache log4j PatternLayout  gt               lt param name  ConversionPattern  value   d ABSOLUTE   5p  t  c 1   L -  m n   gt           lt  layout gt       lt  appender gt        lt root gt           lt level value  debug   gt           lt appender-ref ref  stdout   gt       lt  root gt    lt  log4j configuration gt

User · Answer

This is probably happening because your log4j configuration is set to ERROR  Look for a log4j properties file with contents like the following   log4j rootLogger ERROR  CONSOLE    console logging log4j appender CONSOLE org apache log4j ConsoleAppender log4j appender CONSOLE Threshold DEBUG log4j appender CONSOLE layout org apache log4j PatternLayout log4j appender CONSOLE layout ConversionPattern  d  -5p  -20 20t  -24c 1    m n   The rootLogger is set to ERROR level here using a CONSOLE appender   Note that some appenders like the console appender also have a Threshold property that can be used to overrule the rootLoggers level  You need to check both in this case

User · Answer

This is happening due to the fact that the logging level of your logger is set to  error  - therefore you will only see error messages or above this level in terms of severity so this is why you also see the  fatal  message   If you set the logging level to  debug  on your logger in your log4j xml you should see all messages   Have a look at the log4j introduction for explaination

User · Answer

Here s a quick one-line hack that I occasionally use to temporarily turn on log4j debug logging in a JUnit test  Logger getRootLogger   setLevel Level DEBUG    or if you want to avoid adding imports  org apache log4j Logger getRootLogger   setLevel        org apache log4j Level DEBUG    Note  this hack doesn t work in log4j2 because setLevel has been removed from the API  and there doesn t appear to be equivalent functionality

[java] How to enable Logger.debug() in Log4j

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